The present invention relates to an apparatus for producing a spread fiber bundle and a method for producing a spread fiber bundle using the production apparatus, and further a method for producing a prepreg by impregnating a resin into a spread fiber bundle obtained by the production method.
Prepregs are widely used as intermediate base materials to be molded into aircraft materials, building materials, general industrial materials and sports and leisure articles. A prepreg is produced by a method of paralleling a plurality of fiber bundles, each consisting of a plurality of filaments, in the form of a sheet, thinly and uniformly spreading the plural filaments of the respective fiber bundles in a direction across the parallel direction (transverse direction), and impregnating spaces between the spread filaments with a matrix resin.
Applications of prepregs have been diversified. Prepregs having thin and small irregularity in thickness are demanded. To product such a prepreg, a technique for widely and thinly spreading a fiber bundle without degrading the bundle is necessary.
For spreading a fiber bundle, JP-56-43435-A teaches a method of spreading a fiber bundle, in which the fiber bundle is transferred in contact with plural rollers while being bent around the rollers, and is brought into pressure contact with a cylindrical body vibrating in the axial direction during such transfer operation. YP-61-275438-A discloses a method of spreading a fiber bundle, in which the fiber bundle is transferred in contact with a reciprocating body or rotating body, while being vibrated in the vertical direction, and furthermore brought into pressure contact with a body having a curved surface. JP-7-268754-A proposes a method of spreading a fiber bundle, in which the fiber bundle is transferred in contact with a group of rollers including an eccentrically rotating body, to be spread by means of the eccentrically rotating body.
However, in these spreading methods, the fiber bundle is brought into strong pressure contact with a spreading body The fiber bundle receives a strong abrasive force from the surface of the spreading body, and the abrasion causes several filaments composing the fiber bundle to be broken, thereby generating fuzz in the fiber bundle. In the worst case, the fiber bundle is cut off. Especially to produce a thin prepreg, widely spread thin fiber bundles are needed. In the case where such fiber bundle is produced by any one of the conventional methods, the fiber bundle must be more strongly pressed against the spreading body. In this case, the generation of fuzz in the fiber bundle or the breaking of the fiber bundle becomes a more serious problem.
Such problem becomes especially serious if the fiber bundle is composed of filaments having a high elastic modulus or if the fiber bundle transfer speed is higher. The prepreg produced by using such fiber bundles are low in grade.
To solve such problem, it is proposed to decrease the friction coefficient of the spreading body used for spreading the fiber bundle or to use ultrasonic vibration, but the problem is not sufficiently solved.
It is an object of the invention to provide an apparatus for producing a spread fiber bundle that allows a fiber bundle to be stably and efficiently spread even if the fiber bundle to be spread is composed of filaments having a high elastic modulus or even if the fiber bundle transfer speed (running speed) is high when the fiber bundle is spread, and to provide a method for producing a spread fiber bundle using the production apparatus, and also to provide a method for producing a prepreg by impregnating a resin into spread fiber bundles produced by the production method.
The apparatus for producing a spread fiber bundle of the invention to solve the above problem comprises a group of at least two rollers kept in contact with a running fiber bundle, and a base body reciprocating to be repetitively brought into contact with and kept away from the running fiber bundle as the axial center of said base body moves relatively to the running fiber bundle, said base body being provided between at least a pair of rollers adjacent to each other in said group of rollers.
In the invention, the base body means a member used for spreading a transferred fiber bundle.
Particularly, the base body is a rod circular or polygonal in the cross sectional form (the cross section at right angles to the longitudinal direction). In the case of a polygonal rod, it is preferable that the angles are rounded to some extent.
The base body can be either a fixed body comprising a rod like member supported at both of its end portions without being rotated around the axis in the longitudinal direction thereof or a rotatable body comprising a rod like member supported at both of its end portions rotatably around the axis in the longitudinal direction thereof.
The rotatable body can be either an active rotating body positively driven to rotate or a passive rotating body not positively driven to rotate. In the case of the rotatable body, the base body is usually a rotating roller. The rotating roller used as an active rotating body may be called a driven rotating roller, and the rotating roller used as a passive rotating body may be called a free rotating roller. The rotating body can be either a concentric rotating body in which its rotating axial center is concentric with the peripheral form in the cross sectional form of the base body or an eccentric rotating body in which its rotating axis is eccentric.
The material of the base body can be any material that assures a sufficient strength against repeated contact with and separation from the running fiber bundle, and carbon steel, stainless steel or ceramics can be preferably used.
It is preferable that the surface roughness expressed as the arithmetic mean roughness Ra measured according to JIS B 0601, of the portion of the base body to be kept in contact with the fiber bundles is 0.4 to 3.2. A more preferable range is 0.8 to 1.6.
In the invention, the reciprocation to cause repeated contact and separation means that the base body is reciprocated in such a manner that the state in which the base body is kept in perfect contact with the running fiber bundles (the body contact state) and the state in which the base body is perfectly kept away from the running fiber bundles (the body non-contact state) are periodically repeated.
In the body non-contact state, the running fiber bundle does not receive any pressure from the base body, and are slackened and substantially free from tension partially in the running direction. In this slackened state, the minimum tension acting on spread regions of the fiber bundle is substantially zero.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that the base body is provided together with one or more identical bodies.
A reciprocating direction of the base body is substantially perpendicular to a running direction (a transferring direction) of the running fiber bundle and substantially perpendicular to the widthwise direction of the running fiber bundle. In the case where the running fiber bundle runs in the horizontal direction, the reciprocating direction coincides with the vertical direction.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that the base body is a rotatable roller.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that at least one roller of the group of rollers, or at least one body of the base bodies comprises a roller having a plurality of fiber bundle support portions extending along a direction of the rotating axis of the roller and projected from the surface of the roller, at the periphery of the roller.
In the case where a roller having projected support portions is used, when the running fiber bundle contacts the projected support portions, the running fiber bundle is momentarily held and spread, and the state in which the spread portions are kept into contact with the subsequent projected support portions is sustained. In this state, even if the fiber bundle is falsely twisted, the projected support portions function to prevent the propagation of twisting, and as a result, the fiber bundle spreading action is stabilized.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that at least one of the rollers having projected support portions is positioned upstream of the base body and rotates in the same direction as the running direction of the fiber bundle, with its peripheral surface speed kept lower than the running speed of the fiber bundle.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that at least one of the rollers having projected support portions is positioned upstream of the base body and rotates in the direction reverse to the running direction of the fiber bundle.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that in the roller having projected support portions, the angle (xcex8) formed between the respectively adjacent support portions at the roller axis is 5 to 50 degrees, while the relation between the height of each support portion (t) and the radius of the roller (r) satisfies formula t greater than r[1/cos(xcex8/2)xe2x88x921]. It is more preferable that the angle (xcex8) is 10 to 40 degrees.
In the case where the angle (xcex8) is less than 5 degrees, since the intervals of the respectively adjacent projected support portions are small, the effect of preventing false twisting is small. In the case where the angle (xcex8) is more than 50 degrees, since the curvature of the fiber bundle kept in contact with the projected support portions becomes large, fuzz is likely to be generated in the fiber bundle.
In the case where the relation of formula t greater than r[1/cos(xcex8/2)xe2x88x921] is not satisfied, i.e., in the case of txe2x89xa6r[1/cos(xcex8/2)xe2x88x921], since the fiber bundle contacts the surface of the roller having projected support portions, the effect of preventing false twisting is small.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that at least one roller positioned downstream of the base body, of the group of rollers is a brake roller.
Since the use of a brake roller increases the tension of the fiber bundle after spreading, the running (transfer) of the spread fiber bundle becomes more stable.
In the apparatus for producing a spread fiber bundle of the invention, it is preferable that at least one roller positioned downstream of the base body, of the group of rollers is a dancer roller.
Since the use of a dancer roller decreases the variation in the tension acting on the spread regions of the fiber bundle, the efficiency of the operation to spread the fiber bundle can be enhanced.
The method of producing a spread fiber bundle of the invention for solving the above-mentioned problem comprises the use of the apparatus for producing a spread fiber bundle of the invention and the step of running the fiber bundle zigzag along the rollers of the group of rollers at a fiber bundle running speed of 3 to 20 m/min, with the base body reciprocated at a vibration frequency of 1 to 100 Hz with an amplitude of 1 to 25 mm, for spreading the fiber bundle.
It is preferable that the amplitude of the spreading body reciprocation is 1 to 5 mm. If the amplitude is more than 25 mm, the running of the fiber bundle may become unstable, and in an extreme case, it can happen that the fiber bundle deviates from the predetermined fiber bundle passage.
It is preferable that the vibration frequency of the spreading body is 3 to 60 Hz. If the vibration frequency is more than 100 Hz, fuzz may be generated in the fiber bundle.
To keep the fiber bundle spreading action more stable, it is preferable that the vibration frequency in the reciprocation of the base body increases with the increase of the fiber bundle running speed (transfer speed). It is preferable that if the fiber bundle running speed (transfer speed) is 3 to 10 m/min, the vibration frequency is 3 to 30 Hz, and that if the speed is more than 10 m/min, the vibration frequency is 30 to 60 Hz.
It is preferable that the running speed (transfer speed) of the fiber bundle to be spread is 3 to 20 m/min, and a more preferable range is 5 to 10 m/min. If the fiber bundle running speed (transfer speed) is less than 3 m/min, the spread fiber bundle production efficiency declines, and if more than 20 m/min, the fiber bundle spreading efficiency may decline.
The invention can be preferably used for spreading fiber bundle comprising carbon filaments or graphite filaments, but can also be used for spreading fiber bundle of glass filaments or fiber bundle of organic filaments having a high elastic modulus such as polyaramid filaments.
It is preferable that the number of filaments constituting each fiber bundle is 1,000 to 100,000. A more preferable range is 3,000 to 70,000.
It is preferable that the method of producing a spread fiber bundle of the invention has a step of heating the surface of at least one roller of the group of rollers, or the surface of at least one body of the base bodies, or the fiber bundles per se to a temperature of 70 to 250xc2x0 C.
The fiber bundle may have an oil deposited for improving the bundling property. The fiber bundles to be used for producing prepregs may have a sizing agent deposited for improving the adhesion to the matrix resin.
In the case where the fiber bundle is spread, it is preferable to include a step of heating the fiber bundle using a heating means such as an infrared heater before and/or while spreading, for softening the oil or the sizing agent deposited on the fiber bundle, to enhance the efficiency of spreading action.
The oil or the sizing agent deposited on the fiber bundle can also be decreased or remove, as required, by letting the fiber bundle passes a bath containing an organic solvent or washing solution.
In the case of heating, it is preferable to heat the fiber bundle in a temperature range of preferably 70 to 250xc2x0, more preferably 70 to 180xc2x0 C. in a state to soften the oil or the sizing agent deposited on the fiber bundle.
It is preferable that the method of producing a spread fiber bundle of the invention includes a step of hitting the fiber bundle by means of a reciprocating body or rotating body while heating the fiber bundle at a position upstream of the base body in the running direction of the fiber bundle.
This method promotes the softening of the oil or sizing agent deposited on the fiber bundle.
It is preferable that the method of producing a spread fiber bundle of the invention includes a step of vibrating the fiber bundle at a vibration frequency lower than the reciprocating vibration frequency of the base body by means of a reciprocating body or rotating body at a position upstream of the base body in the running direction of the fiber bundle.
This method slackens the fiber bundle in the state where the fiber bundle is kept away from the spreading body (non-contact state), to promote the spreading action. It is preferable that the vibration frequency lower than the reciprocating vibration frequency of the spreading body is 0.5 to 5 Hz, and a more preferable range is 1 to 3 Hz. In this case, it is preferable that the amplitude of vibration is 20 to 200 mm.
In the method of producing a spread fiber bundle of the invention, it is preferable that the tensile modulus of elasticity of the fiber bundle is 200 to 700 GPa.
The fiber bundle having a tensile modulus of elasticity of 350 to 700 GPa gives a better effect in the invention.
It is preferable that the method of producing a spread fiber bundle of the invention includes a step of blowing a gas to the running fiber bundle at a position at least either upstream or downstream of the base body in the running direction of the fiber bundle.
In the method of producing a spread fiber bundle of the invention, it is preferable that the temperature of the gas is 70 to 250xc2x0 C. and that the gas blowing pressure is 0.1 to 0.5 MPa.
The gas can be blown at a position upstream or downstream of the base body in the running direction of the fiber bundle (transfer direction) However, if it is blown at a position upstream, the effect of spreading the fiber bundle can be further enhanced.
The gas blow gives an effect of spreading the fiber bundle more efficiently even in the case where the fiber bundle is strongly bundled due to the deposition of oil or sizing agent.
It is preferable that the temperature of the gas is 70 to 180xc2x0 C., and that the gas blowing pressure is 0.2 to 0.5 MPa. The gas usually used is pressurized air, and the pressurized air can be supplied from a pressurized air source usually available in the production factory.
It is preferable that the method of producing a spread fiber bundle of the invention includes a step of supporting the fiber bundle on a belt having a width wider than the fiber bundle width and curved to be projected on the side to be kept in contact with the fiber bundle, at a position downstream of the base body in the running direction of the fiber bundle.
The use of the belt is effective for further enhancing the effect of spreading the fiber bundle.
As the supply source of the fiber bundle to be spread, usually bobbins having fiber bundle wound around them and installed on a creel are used. In this case, it is preferable that the resistance against the running fiber bundle, of the mechanism for supplying the fiber bundles from the bobbins, is changed as required for stabilizing the spread state of fiber bundle.
The method of producing a prepreg of the invention comprises the step of impregnating a resin into the spread fiber bundles produced according to the method of producing a spread fiber bundle of the invention
The prepreg production method allows the production of a prepreg with a high grade that is small in thickness irregularity though the thickness is thin, and has a resin sufficiently impregnated in the filaments.
The resin used and the resin impregnation method are not especially limited. Examples of the resin include thermosetting resins such as epoxy resins, vinyl ester resins, unsaturated polyester resins and phenol resins, thermoplastic resins such as polyester resins, polyethylene resin, polycarbonate resins, polyether resins and polyamide resins, etc. An epoxy resin is often used.
Examples of the epoxy resin include bisphenol A epoxy resin, phenol novolak epoxy resin, cresol novolak epoxy resin, glycidylamine epoxy resin, alicyclic epoxy resin, urethane modified epoxy resin, brominated bisphenol A epoxy resin, etc.
One of these epoxy resins can be used, but two or more of them can also be used together. Furthermore, a liquid epoxy resin or a solid epoxy resin can also be used as it is. Usually, a curing agent is added to the epoxy resin used.
For impregnation, for example, a resin lowered in viscosity by heating or dissolving in a solvent can be impregnated into the fiber bundles. As another method, the fiber bundles can be held between two resin sheets respectively obtained by thinly and uniformly applying a resin to such a sheet as paper or resin film treated to be releasable, and the laminate is pressurized using a heating roller, etc.